Automatic volume regulation of transmission systems



Dec. 15, 1925- s. B. WRIGHT AUTOMATIC VOLUME REGULATION OF 'rmmsmsszonSYSTEMS Filed Sept. 5, 1924 mRNEY Patented Dec. 15, 1925.

UNITED STATES PATENT OFFICE.

SUMNER B. WRIGHT, OF EAST ORANGE, JERSEY, ASSIGNOR TO AMERICAN TELE-PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

AUTOMATIC VOLULIE REGULATION OF TRANSMISSION SYSTEMS.

Application filed September 3, 1924. Serial No. 735,661.

To all whom it may concern:

Be it known that I, SUMNER B. WRIGHT, residing at East Orange, in thecounty of Essex and State of New Jersey, have invented certainImprovements in Automatic Volume Regulation of Transmission Systoms, ofwhich the following is a specification.

This invention relates to transmission circuits and more particularly toarrangements to automatically change the volume of the currentstransmitted as the intensity of the signal varies.

In transmission systems such as are used in connection with radiobroadcasting; public address and other similar systems it is frequentlydesirable to change the range of volume transmitted. For example, intransmitting musical productions the volume of the signal may vary frominstant to instant over a range, the maximum power of which bears aratio of as high as'100,000 to the minimum power. In many instances, itis impractical to transmit such a wide range of variation involumeeither because of some limitation in the transmission medium orbecause of some limitation in a translating device in the transmissionsystem.

It has heretofore been necessary to change the volume to be transmittedfrom time to time in case it became too great or too small, this changebeing effected by some manual manipulation. This involved obviousdifliculties, for the attendant must not only make the change at theproper instant but will have to depend upon his own individual judgmentas to how great a change in volume cuit is illustrated conventionally,the particular circuit shown being of the type .known as a publicaddress system. The system involves a source of sound X in the vicinityof which a sensitive pick-up trans-- mitter B is located, the pick-uptransmitter being connected through an amplifier R and a power amplifierR, to a loud speaker LS. The pick-up transmitter as illustrated is ofthe well known push-pull type and is connected through the usualbalanced transformer arrangement 10 to the amplifier R. The amplifiersRand R may be of any well known type, such, for example, as vacuum tubeamplifiers.

In order to control the volume transmitted to the loud speaker LS fromthe transmitter B a variable shunt comprising resistances 1' r r 1' and7- is bridged across the cir cuit at a point intermediate between theamplifiers R and R The total shunt resistance across the circuit may bevaried by cutting in a greater or lesser number 01 the resistances 1, tor, in a manner about to be described, thereby varying the volumetransmitted to the power amplifier R and consequently to the loudspeaker LS.

In order to automatically control the volume, an auxiliary or controltransmitter A, which may be of the same type as the transmitter B, isassociated with an auxiliary control amplifier R, which may be similarto the amplifier R, already described, the circuit connectionscomprising a transformer 11 and other elements similar to thoseassociated with the pick-up transmitter. The output circuit of theamplifier R has associated therewith a number of amplifier detectorarrangements such as D D D and D,. These amplifier detector arrangementsare schematically illustrated, but may comprise any known type of devicefor amplifying the alternating voice currents and rectifying ordetecting the voice currents so as to translate them into direct currentcomponents having amplitudes corresponding to the intensity of thealterating currents.

Each of the amplifier detector units has a sensitive relay connectedtherewith, as illustrated at S S S and S,,. These relays are marginal sothat they will respond to different current values. The'relay S forexample, may respond to very minute cur-' rents and the relay S, to onlythe very largest currents resulting from signal transmission, while therelays S and S may respond to intermediate current values. Each of therelays S to S, inclusive, by means of; a contact, short-circuits one ormore of the resistances r, to 1' inclusive. In order that the amplifierdetector circuits shall not pro duce an undue shunting effect upon eachother their input circuits may preferably be of high impedance. p

The operation is as follows: Assuming that the intensity of the signalat X has a minimum value, the control transmitter A and the pickuptransmitter B will both operate to generate alternating currents ofsmall amplitude. The, alternating currents generated by the transmitterA are amplified by the amplifiers R and impressed upon the amplifierdetectors 1), to D inclusive so that rectified currents flow through thewindings of the relays S, to S, inclusive. These rec tified currentswill be of such small amplitude that none of the relays S to S inclusivewill be sufliciently energized to attract its armature; consequently,the shunt circuit bridged across the input side of the repeater R, willinclude all of the resistances 1', to r, inclusive. As these resistanceswill be in series with each other the resistance of the shunt will bevery large so that substantially the entire alternating currentgenerated by the pick-up transmitter B and amplified by the amplifier Rwill be transmitted to the input circuit. of the power amplifier R,. Ifan instant later the intensity of the signal at the source X shouldincrease, the rectified currents flowing through the relays S, to Sinclusive will be increase-d so that one or more of the relays S, to Swill be operated. depending upon the intensity of the signal. If onlythe relay S is operated the resistance 1", will be short-circuited andthe shunt circuit bridged across the input side of the amplifier R, willbe reduced, with a corresponding reduction in the amplitude of thecurrents impressed upon the amplifier. If the rectified currents aresufiicient in intensity to operate both relays S and S resistances r,and 1', will both be short-circuited and the shunt will only include theresistances 1' 1' and 1",, in series. The amplitude of the currentstransmitted to the repeater R will accordingly be further decreased.Similarly, if the signal is of maximum intensity the rectified currentswill be of such amplitude that all of the relays S to S, inclusive areoperated so that the resistances r, to 1", will be short-circuited andthe shunt connection will only include the of resistance shunted acrossthe input of the amplifier R, will be just sufiicient to main- .tain theactual value of the current impressed upon the power amplifier R ofminimum value, with the result that although the intensity of the signalat the source may change, the signal emitted by the loud speaker will beof constant volume. If the resistance 1",, be made very small, or evenzero, and the other resistances be progressively larger, it will beapparent that as the intensity of the sound increases a greaterproportion of the energy transmitted from the amplifier R will beby-passed through v the shunt, with the result that the sound emitted bythe loud speaker will decrease in volume as the sound at the sourceincreases in volume. the resistances 1', to rinclusive are all madefairly large and properly related to each other, the effect may bemadesuch that for a signal of minimum amplitude no change in the volumeof current emitted by the loud speaker will be produced, but as thesignal increases in volume a sufficient amount of resistance willbeincluded in the shunt circuit so that the signal emitted by the loudspeaker, while increased in volume, will not be increased as much as theoriginal source itself.

Inasmuch as a certain time will be required for the relays such as S toS inclusive to operate in response to a change in volume, some provisionmust be made to enable the relays to operate and change the value of theresistance of the shunt circuit just at the instant, or just before theinstant, that the currents from the pick-up transmitter B arrive at theshunt. This may be readily accomplished by arranging the controltransmitter A somewhat nearer to the source ofsound than the pick-uptransmitter B. Sound travels through the air slower than the electriccurrents are transmitted over the circuits and consequently, by properlylocating the transmitter B, sufficient time may elapse while the soundis being transmitted through the air to enable the transmitter A toactuate the relays S to S inclusive. For example, on the assumption thatsound travels 1180 feet per second in air, if the transmitter B is 12feet further away from the source of sound X than the transmitter A, oneone-hundredth of a second will elapse after the sound strikes the On theother hand, if V transmitter A before it will actuate the trans mitterB, thus giving the relays S to S, inclusive suflicienttime to operateand regulate the loss in the transmission circuit between the amplifiersR and R It will be obvious that the general principles herein disclosedmay be embodied in many other organizations widely difierent from thoseillustrated without departing from the spirit ofi the invention as de-'fined in the following claims.

What is claimed is:

1. In a signaling system, means to translate signaling energy intoelectrical energy having variations of volume, a transmission .eircuitupon which said electrical energy may be impressed, and meansautomatically responsive to a change in the volume of said electricalenergy to so change the volume of the energy transmitted that it willvary through a range different from that of the impressed energy, thevariations in volume of the transmitted energy remaining proportional tothe variations in volume of the impressed electrical energy.

2. In a signaling system, means to generate signaling energy havingvariations of volume extending over a wide range, a transmission circuitover which a lesser range of volume is to be transmitted, means toimpress said energy upon such transmission circuit, and meansautomatically responsive to changes in the volume of the generatedenergy to reduce the volume of the energy transmitted so that the rangeof volume transmitted will be less than the range of volume generated,the variations in volume of the transmitted energy remainingproportional to the variations in volume of the generated energy.

3. In a signaling system, means to generate signaling energy havingvariations of volume, a transmission'circuit including a pick-up meansresponsive to said energy, a variable loss element included in saidtransmission circuit, and means to automatically vary the lossintroduced by said element as the volume of the generated energy varies,so that the volume of the energy transmitted will vary through a rangedifferent from that generated, the variations in volume of thetransmitted energy remaining proportional to the variations in volume ofthe generated energy. 7

4. In a signaling system, means to generate signaling energy havingvariations of volume, a transmission circuit including a pick-up meansresponsive to said energy, a variable shunt bridged across thetransmission circuit, and means to vary the electrical values of saidshunt automatically in response to variations of the energy generated,so that the volume of the ener transmitted will vary through a rangeiiififerent fromthat generated, the variations in volume of thetransmitted energy remaining proportional to the variations in volume ofthe generated energy 5. In a signaling system, means to generatesignaling energy having variations of volume, a transmission circuitincluding a pick-up transmitter responsive to said energy, a variableloss element included in said transmission circuit, an auxiliarytransmission circuit over which currents corresponding to the signalingenergy generated may be transmitted, and means associated with saidauxiliary circuit for automatically operating in response to variationsin the amplitude of the current transmitted over said auxiliary circuitto variably adjust the loss element in said first mentioned transmissioncircuit.

6. In a signaling system, means to generate signaling energy havingvariations of volume, a main transmission circuit including a pick-uptransmitter responsive to said energy, a variable loss elementassociated with said circuit, an auxiliary transmission circuitincluding a second transmitter responsive .to said energy, and meansassociated with-said second circuit and responsive to currents generatedby said second transmitter to variably control the loss introduced intosaid first circuit by said loss element as the volume of the generatedenergy varies.

7. In a signaling system, means to generate signaling energy havingvariations of volume, a main transmission circuit including a pick-uptransmitter responsive to said energy, a variable loss elementassociated with said circuit, an auxiliary transmission circuitincluding a second transmitter responsive to said energy, and meansassociated with said second circuit and responsive to currents generatedby said second transmitter to variably control the loss introduced intosaid first circuit by said loss element as the volume of the generatedenergy varies, said second transmitter being located nearer the sourceof sound than the said first transmitter to enable the variable losselement to be adjusted in response to a change in the volume of theenergy generated before the corresponding currents have been transmittedfrom said first transmitter to said'loss element.

8. In a signaling system, means to generate signaling energy havingvariations of volume, a transmission circuit upon which the energy maybe impressed, means associated with said circuit for automaticallyvarying its transmission efiiciency as the energy generated varies involume, and means to introduce a sufficient delay in transmission oversaid circuit to enable said automatic varying means to operate inresponse to a given change in volume before the corresponding currentsarrive.

9. In a signaling system, means to generate signaling energy havingvariations in volume, a transmission circuit upon which said energy maybe impressed, a variable transmission element in said circuit, meansautomatically responsive to changes in the volume of the energygenerated to adjust said variable transmission elements; and means todelay the transmission of currents over said transmission circuit by asufiicient amount to enable said automatically responsive means toadjust said variable transmission element before said currents arrive atsaid variable transmission element.

In testimony whereof, I have signed my name to this specification this2nd day of September 1924.

SUMNER B. WRIGHT.

